import java.util.Random;

public class eg7_8 {
    public static void main(String[] args) {
        String yzmStr = "0123456789abcdefghijklmnopqrstuvwxyz";
        StringBuilder sBlider = new StringBuilder(4);
        char[] yzmArr = yzmStr.toCharArray();
        Random rand = new Random();
        for (int i = 0; i < 10; i++) {
            for (int j = 0; j < 4; j++) {
                int pos = rand.nextInt(36);
                sBlider.append(yzmArr[pos]);
            }
            System.out.println("第" + (i + 1) + "个验证码为：" + sBlider.toString());
            sBlider.setLength(0); // 或者 sBlider.delete(0, sBlider.length());
        }
    }
}